Current IR imaging devices employ mechanical modulators to block incoming IR radiation by dropping a shutter. The purpose is often to enable background measurements to taken, which can be employed to enhance an IR image. However, the speed of such mechanical shutters is limited and the structure is typically bulky and noisy when in use.
There are also known attempts to provide modulators exploiting the Kerr effect, liquid crystals and acousto-optical characteristics. However, these are not widely implemented for the reasons explained below.
Kerr effect modulators are fast, but usually have bulky dimensions, a small aperture and require the application of high voltages. However, the major drawback with Kerr effect modulators is that they are birefringent.
For infrared light modulation an active layer consisting of liquid crystals must be relatively thick, corresponding to the wavelength to be absorbed. This results in poor response to applied pulses and a low extinction ratio. Almost all types of liquid crystals show slow response, narrow bandwidth and birefringence.
Acousto-optical modulators usually do not consume electrical power significantly and have good extinction ratio, but they are bulky in comparison to devices in microelectronics, have low bandwidth and relatively slow response in modulators with large apertures.
An aim of the present invention is therefore to provide an optical absorber which can be employed in an electro-optical modulator and which helps to address the above-mentioned problems.